Electronic devices may have several different layers made of different materials and/or having different geometries. Fabricating such devices usually involves the patterning of several layers of thin films on a substrate. The use of a shadow mask to deposit such patterned thin films on the substrate is well known to the art. A "shadow" mask is a mask having apertures through which material is deposited onto a substrate, as opposed to an optical mask, which is used to selectively expose photoresist on a substrate to radiation.
In most devices, it is important that each patterned layer is fabricated in a particular position relative to previously fabricated layers. This alignment between layers is usually achieved by reference to features on the substrate, such as alignment markers previously fabricated on the substrate, that can be matched with features on the mask, such as a similar alignment marker. However, the alignment process is usually repeated for each layer that has a pattern and/or position different from that of the previously deposited layer, and each alignment involves additional cost and effort.
Alignment usually involves moving the mask relative to the substrate while viewing alignment markers on the mask and substrate under a microscope. Assuming that the mask and substrate are parallel, there are three types of movement: x, y, and .THETA., where x and y represent linear movement parallel to the plane of the mask and substrate, and .THETA. represents rotation in the plane of the substrate. Mechanisms are known to the art for achieving such movement with a great deal of accuracy. Modem semiconductor fabrication techniques can be used to control movement with an accuracy of about 0.1 micron. Stacked coarse and fine movement piezo electric materials can be used to achieve such movement on the order of hundreds of microns or more, with an accuracy measured in tenths of a micron. X-y translators, which have very fine screws that may be turned by hand or by step motors to move a stage, can be used to achieve such movement on the order of hundreds of microns with an accuracy measured in microns. It is anticipated that advances in technology will enable movement to be controlled with greater accuracy, and that such advances can be used with the present invention. A rough alignment, usually involving a stage that can be moved linearly and in rotation through the use of screws, may be performed to bring the misalignment between the mask and substrate within the range of motion of a more accurate alignment mechanism. While alignment processes may be automated to some degree, each alignment involves cost and effort. Also, each additional alignment may introduce errors into the device to be fabricated.
It is sometimes desirable to fabricate a device from multiple materials, where the different materials have similar, but not identical, shapes, sizes and/or positions. It is known to deposit two or more such materials through the same shadow mask. For example, Miyaguchi et al., Organic LED Full Color Passive-Matrix Display, 9th International Workshop on Inorganic and Organic Electroluminescence, Extended Abstracts p. 127, Bend, Oreg., Sep. 14-17, 1998, discloses a multi-color passive-matrix display that uses three different organic materials to emit three different colors of light. These different organic materials are sequentially deposited through the same shadow mask, where the mask is moved in between depositions. However, the reference does not disclose how the position of the mask controlled.
The position of layers deposited through the same photoresist may be varied by varying the angle from which deposition occurs, as described by Burrows et al., "Method of Fabricating and Patterning OLEDs," patent application Ser. No. 08/977,205, filed on Nov. 24, 1997, and Forrest et al., "Method for Deposition and Patterning of Organic Thin Film," patent application Ser. No. 08/976,666, filed on Nov. 24, 1997, which are incorporated by reference. However, it is difficult to achieve uniform deposition onto an angled substrate over a wide area, unless the source to substrate distance is much greater than the size of the substrate, which would require a very large vacuum chamber.